At KMS we use standards based grading. That means that every grade in the gradebook is based on students' ability to show mastery of one skill (standard, learning goal, etc.). Learners can earn a 1-4 on a skill. A 3 means that the student has mastered the skill. Then kids' scores are averaged to provide an overall report card grade.
Here are some videos that help explain standards based grading in different ways: